A solid consists of a cone on top of a cylinder with a radius equal to that of the cone. The height of the cone is 36 and the height of the cylinder is 8 . If the volume of the solid is 64 pi, what is the area of the base of the cylinder?

1 Answer
Nov 16, 2016

20.1

Explanation:

A Conical Volume is given by:
V = 1/3 * pi * r^2 * h
A Cylindrical Volume is given by:
V = pi * r^2 * h
Circular Area (base of cylinder)
A = 2*pi * r^2

Total solid volume =
64pi = 1/3 * pi * r^2 * h_1 + pi * r^2 * h_2

Solve for r.
64 = 1/3 * r^2 * 36 + r^2 * 8 ; 64 = r^2 * 12 + r^2 * 8
64 = r^2 * 20 ; 64/20 = r^2 ;

r^2 = 3.2 ; r = 1.79

A = 2*pi * 3.2 = 20.1